This invention relates to a novel method of depositing diamond or diamond-like substances in a microwave plasma chemical vapor deposition system to produce a film having superior field emission properties.
Diamond and diamond-like carbon (DLC) thin films have recently attracted much attention due to their potential applications in vacuum microelectronics. Apart from their excellent properties such as good thermal conductivity, chemical inertness and high breakdown electric field, diamond and DLC thin films have been found to have excellent field electron emitting properties. It has been suggested that it is possible to use a form of amorphous carbon known as xe2x80x9camorphic diamondxe2x80x9d as a planar cold cathode in a novel form of field emission display (FED), which is much simpler and cheaper than the metal or Si tip arrays commonly used as large area cold cathodes. The direct use of diamond or DLC films as planar cathodes, however, has been hindered by poor uniformity of field emission from these films. This has led to extensive studies into diamond and DLC thin film processing methods and attempts to understand field emission mechanisms of these films.
It is known that diamond nucleation density in a Carbon Vapor Deposition (CVD) growth environment can be enhanced by a bias induced nucleation method. This process involves applying a negative or positive voltage to the substrate in a CH4/H2 plasma, where positive ions or electrons are attracted towards the substrate surface. The interaction between ions or electrons and the surface is believed to create active sites for nucleation. It is known that a negative bias has a number of effects on the nucleation process, such as a) acceleration of migration and carbonization reaction, b) transition from sp2 carbon bonds to sp3 bonds and c) sub implantation of ions.
Recently, it was reported that (001) textured diamond films can be deposited on a (111) surface using a proper negative bias during nucleation. However, our invention refers to films deposited where the negative bias on the substrate is maintained through the entire growth phase, resulting in superior field emissioni characteristics. Ion bombardment has been widely used to modify the properties of growing films, but little is known of the effect of ion bombardment with a negative substrate bias maintained during the entire time of growth on field emission properties of diamond thin films. We deposited diamond films on Si wafers under various substrate bias conditions in a CH4xe2x80x94N2xe2x80x94H2 plasma and determined the influence of the CH4 concentration and the bias (+100 V to xe2x88x92150 V) on field emission performance. We found that providing a negative substrate bias during the entire growth process resulted in a film with superior field emission properties as measured by turn-on field voltages of 1.5-2.0 v/xcexcm and low work function. Accordingly, it is an important object of the present invention to provide a method of producing diamond or diamond like films comprising establishing a negative bias on a substrate with an electrically conductive surface in a microwave plasma chemical vapor deposition system with the atmosphere subjected to the microwave energy including a source of carbon, nitrogen, hydrogen and possibly Ar, maintaining the negative bias on the substrate through both the nucleation and growth phase of the film until the film is continuous.